For about the last fifty years, protective and decorative coatings based upon acrylic polymers have been increasingly used. These polymers have been utilized in many applications because they have provided a wide range of strength, flexibility, toughness, adhesion, degradation resistance and other film properties. Many acrylics, however, are solution polymers because they are prepared and applied as solutions of organic polymers in organic solvents. In coatings technology, polymeric vehicles which included thermoplastic acrylic polymers required the use of organic solvents which often are toxic and/or subject to regulation that demand their reduction in coating compositions.
Environmental concern has become increasingly important. This concern not only extends to preservation of the environment for its own sake, but extends to safety for the public as to both living and working conditions. Volatile organic emissions resulting from coating compositions which are applied and used by industry and by the consuming public are often not only unpleasant, but contribute to photochemical smog. Governments have established regulations setting forth guidelines relating to volatile organic compounds (VOCs) which may be released to the atmosphere. The U.S. Environmental Protection Agency (EPA) has established guidelines relating to the amount of VOCs released to the atmosphere, such guidelines being scheduled for adoption by the states of the United States. Guidelines relating to VOCs, such as those of the EPA, and environmental concerns are particularly pertinent to the paint and industrial coating industry which uses organic solvents which are emitted into the atmosphere.
The use of water based polymeric vehicles, or alternatively, high solids polymeric vehicles are two general approaches that have been used to reduce VOCs. Aqueous systems have limited the molecular weights of the polymers used in the polymeric vehicle, which limited the hardness and other properties of the coating binders and films which resulted from the polymeric vehicles. Moreover, high levels of coalescents often have been required in aqueous thermoplastic vehicles. In water reducible cross-linkable systems, as opposed to aqueous thermoplastic emulsions, molecular weights of polymers have been kept low and have required cross-linking.
The high solids approach often includes organic solvents or powder coatings. High solids, however, present problems in disposition of the polymeric vehicle. In powder systems requiring heat, disposition efficiency often is less and use of more than one color is difficult. Other high solids systems also may require specialized equipment because of the high solids content and the use of at least some organic solvents which are VOCs.
It is an object of this invention to provide water dispersions of high molecular weight acrylic polymers which dispersions have low VOCs.
It also is an object of this invention to provide a process for making aqueous dispersions of amine salts of high molecular weight acrylic polymers.
It is a further object of this invention to provide a low VOC thermoplastic or cross-linkable polymeric vehicle which includes a high molecular weight acrylic polymer.
Still further objects and advantages of the invention will be found by reference to the following description.